Doing the C2work scheme and voucher arrives this monday for £1,000. We are allowed to top up.

Basically I have my heart set on this:

2013 Flash 2 alloy £999
CANNONDALE F29 2 (FLASH ALLOY) 2013 :: £999.99 :: Mountain Bikes :: Front Suspension 29ers :: Pauls Cycles

However only Medium or Large left. I am about 5'5 with a 29 inch inseam.

I went to a LBS and they had a 2015 C'dale trail in medium, which seemed a little too big. My previous bike was a 2009 Boardman Pro (Hardtail) in a size medium which was around a 17 inch frame from what I can remember.

There is also:
2013 Flash 1 alloy £1,129.99
CANNONDALE F29 1 (FLASH ALLOY) 2013 :: £1129.99 :: Mountain Bikes :: Front Suspension 29ers :: Pauls Cycles

This model is available in small and medium.

As the bike is on sale, the £1000 voucher is worth £900 (£100 as admin cost). So I am looking to see what you guys think:

Go for the medium and spend £100 to get to the £1000 price OR get the small in the Alloy 1, and have to fork out an additional £230.00.

Preferably I'd prefer to just have to fork out the £100 and get the Alloy 2.

I'd love to hear from anyone that has this model, or a newer model of the same bike and see what they think - the top tube looks like it slopes downwards towards the seat from every youtube vid Ive found and looks like Id get away with the Medium...but the standover when I tried the Trail 5 in the LBS was non-existant and that was a 650b instead of the 29ers Im looking at here.

Any help would be extremely appreciated as Ive not owned nor have any mates who own a c'dale so Im struggling to get help with this. I am 75% sure I could get away with the medium but as I cant try it and its a Mail order - I dont want to go in totally blind..!